Rebonded fusion-cast AZS refractory grain

Abstract

Fired refractory articles are made of a shaped refractory composition predominantly comprising grain of fusion-cast AZS refractory having: (i) a three-phase microstructure of interlocking crystals of corundum (alpha alumina) phase and baddeleyite (zirconia) phase with intercrystalline glassy phase therebetween, the glassy phase being about 15-30 vol.% of the AZS refractory, and (ii) an oxide analysis consisting of 35-60 wt.% Al.sub.2 O.sub.3 plus Cr.sub.2 O.sub.3 with Cr.sub.2 O.sub.3 .ltoreq. 60 wt.% of Al.sub.2 O.sub.3 plus Cr.sub.2 O.sub.3, 25-50 wt.% ZrO.sub.2, 10-18 wt.% SiO.sub.2, 0.8-1.8 wt.% Na.sub.2 O plus K.sub.2 O, and up to 0.7 wt.% other ingredients (e.g. impurities). Refractory composition consists of: (A) 25-60 wt.% fusion-cast AZS refractory coarse grain being at least 89 wt.% -6+20 Tyler mesh, (B) 0-38 wt.% fusion-cast AZS refractory medium grain being at least 73 wt.% -10+35 Tyler mesh, and (C) 30-50 wt.% at least one component selected from the group consisting of: (1) 0-50 wt.% fusion-cast AZS refractory fine grain being at least 60 wt.% -35+325 Tyler mesh and (2) 0-30 wt.% at least one constituent selected from the group consisting of: (a) alumina being at least 90 wt.% -325 Tyler mesh, at least 98.5 wt.% Al.sub.2 O.sub.3 and not more than 0.5 wt.% Na.sub.2 O, and (b) -325 Tyler mesh chromic oxide being at least 95 wt.% Cr.sub.2 O.sub.3, and (D) 0-7 wt.% colloidal silica.

Description

BACKGROUND

The field of the invention relates to refractory compositions for sintered refractory articles formed with predominantly grain of fused AZS (alumina-zirconia-silica) material, particularly fusion-cast AZS refractory solidified and cooled as a unitary mass or block in a relatively slow manner and thereafter crushed into grain to be rebonded.

The general concept of rebonding crushed fused AZS grain was apparently first disclosed in U.S. Pat. Nos. 1,240,490 and 1,240,491. The rebonding was to be accomplished by ordinary ceramic bonds (cf. the clay-flux bond in U.S. Pat. No. 930,376). For refractories, it was noted that the fused AZS composition could contain zirconia up to equimolecular proportion with alumina (ca. 54.7 wt.% ZrO.sub.2 and 45.3 wt.% Al.sub.2 O.sub.3 when ignoring impurities).

A somewhat similar teaching is presented in U.S. Pat. No. 1,324,546 although the composition of the fused AZS grain apparently includes a substantial amount of MgO. Besides the fused grain and clay-flux bond, it is noted that finely ground unfused materials of the same composition as the fused grain may also be added. The refractory products are said to have resistance to corrosive and erosive action of molten material (e.g. molten metals or glass) in contact therewith, to deformation at high temperature and to cracking during changes of temperature.

It was later recognized that the clay-flux bonds of those early rebonded fused AZS grain refractories significantly limited refractoriness and resistance to chemical action. As a result, efforts were made, as noted in U.K. Pat. Nos. 605,215 and 610,334, to form rebonded refractories solely of fused AZS grain, initially with normal fusion-cast material and then with rapidly cooled grain formed by dispersing a melt into droplets, or of fused AZS grain combined with another fused grain where the glassy phase of one was more refractory than the glassy phase of the other. However, no apparent special effort was made to control particle sizing other than to provide a mixture of granules and fine particles.

In more recent times, several particular compositions have been developed for producing refractory articles with rebonded fused AZS grain for resisting contact action of molten materials and thermal shock. Each one requires a different special combination of materials for proper attainment of suitable properties. U.S. Pat. No. 3,567,473 prescribes mixing certain fused AZS grain with either tabular alumina plus alpha quartz or kyanite as well as with calcined alumina, magnesium oxide and colloidal silica, each in particular proportions. U.S. Pat. No. 3,782,980 prescribes mixing certain fused AZS grain with an essential proportioned combination of zircon (or zirconia) and alumina. U.K. Pat. No. 1,429,723 prescribes combining certain fused AZS grain with alumina and/or mullite together with some silica binder. U.S. Pat. No. 3,846,145 prescribes certain fused AZS grain to be combined with kyanite, zircon, calcined alumina, chromic oxide and silica.

It has also been proposed in U.K. Pat. No. 1,254,792 to provide a binder (or mortar) of fusion-cast AZS grain mixed with either hydraulically setting cement, expanded clay or chemical binder to join relatively small fusion-cast slabs together to form a composite refractory block.

None of these prior art rebonding compositions are seen to comprehend the unique balanced combination refractory composition of the invention disclosed and claimed herein, which is believed to provide superior properties to those of these prior art compositions.

SUMMARY OF THE INVENTION

The invention is a refractory composition for making refractory articles and the fired refractory article made of such refractory composition. Such fired article, vis a vis present competitive prior art bonded refractories, is characterized by superior resistance to corrosion by molten glass and alkali in contact therewith and by superior flexure strength (i.e. modulus of rupture or MOR) at room temperature before and, in many cases, after substantial thermal cycling. The fired article of this invention is also characterized by good thermal shock resistance and other properties which will be apparent from the following disclosure herein.

The unique balanced combination refractory composition is provided with grain of fusion-cast AZS refractory having an important substantial volume amount of glassy phase that undergoes solid state reaction with other ingredients of the composition during firing thereof to yield formation of substantial mullite phase, within both the fusion-cast grains themselves and the glassy matrix bonding them together, and reduced glassy phase, which is believed to contribute substantially to the attainment of the improved properties. Such glassy phase in the fusion-cast AZS refractory results mainly from properly balanced amounts of SiO.sub.2, Al.sub.2 O.sub.3, Na.sub.2 O, K.sub.2 O and other ingredients (e.g. impurities) residing in the glassy phase. Also importantly contributing to the improved fired product properties, as part of the unique balanced combination, is the controlled grain or particle sizing and the controlled combination of materials in the refractory composition.

In its broadest aspect, the refractory composition consists of:

(A) 25-60 wt.% fusion-cast AZS refractory coarse grain being at least 89 wt.% -6+20 Tyler mesh,

(B) 0-38 wt.% fusion-cast AZS refractory medium grain being at least 73 wt.% -10+35 Tyler mesh, and

(C) 30-50 wt.% at least one component selected from the group consisting of

(1) 0-50 wt.% fusion-cast AZS refractory fine grain being at least 60 wt.% -35+325 Tyler mesh, and

(2) 0-30 wt.% at least one constituent selected from the group consisting of

(a) alumina being at least 90 wt.% -325 Tyler mesh, at least 98.5 wt.% Al.sub.2 O.sub.3 and not more than 0.5 wt.% Na.sub.2 O, and

(b) -325 Tyler mesh chromic oxide being at least 95 wt.% Cr.sub.2 O.sub.3.

The fusion-cast AZS refractory of the grains in the refractory composition has a three-phase microstructure of interlocking crystals of corundum (alpha alumina) phase and baddeleyite (zirconia) phase with intercrystalline glassy phase therebetween. The glassy phase is about 15-30 (preferably 20-30) volume % of the fusion-cast AZS refractory. The oxide analysis of the fusion-cast AZS refractory consists of (in wt.%):

______________________________________ Al.sub.2 O.sub.3 Other Range +Cr.sub.2 O.sub.3 ZrO.sub.2 SiO.sub.2 Na.sub.2 O+K.sub.2 O Ingredients ______________________________________ Broad 35-60 25-50 10-18 0.8-1.8 up to 0.7 Preferred 40-55 30-45 10-16 1.0-1.6 up to 0.5 ______________________________________

with the Cr.sub.2 O.sub.3 being equal to or less than 60 wt.% (preferably 50 wt.%) of Al.sub.2 O.sub.3 plus Cr.sub.2 O.sub.3. Based on present economic reasons, it is preferred to omit Cr.sub.2 O.sub.3. A particular desired fusion-cast AZS refractory has an oxide analysis consisting of 45-50 wt.% Al.sub.2 O.sub.3, 33-41 wt.% ZrO.sub.2, 12-16 wt.% SiO.sub.2, 1.1-1.5 wt.% Na.sub.2 O and up to 0.3 wt.% other ingredients.

The fired refractory article made of the above-described refractory composition has a four-phase microstructure of corundum, baddeleyite, mullite and glassy phase with the mullite being about 5-25 wt.% (preferably 8-22 wt.%) thereof and the glassy phase being about 5-20 volume % (preferably 5-17 volume %) thereof.

As used herein, corundum phase includes the corundumtype phase of Cr.sub.2 O.sub.3 in solid solution with Al.sub.2 O.sub.3.

For making pressed refractory shapes, an especially desired modification of the foregoing refractory composition has:

(A) the coarse grain being 33-37 wt.%,

(B) the medium grain being 20-25 wt.%, and

(C) the at least one component being 40-45 wt.% selected from the group consisting of

(1) 15-45 wt.% the fine grain and

(2) 0-30 wt.% the at least one constituent selected from the group consisting of

(a) the alumina which is at least 98.5 wt.% Al.sub.2 O.sub.3 and

(b) the chromic oxide which is at least 95 wt.% Cr.sub.2 O.sub.3.

For making cast refractory shapes, the broadly described refractory composition is desirably modified so as to have:

(A) the coarse grain being 33-37 wt.%,

(B) the medium grain being 32-37 wt.%, and

(C) the at least one component being 30-35 wt.% selected from the group consisting of

(1) 0-25 wt.% the fine grain and

(2) 10-30 wt.% the at lest one constituent selected from the group consisting of

(a) the alumina which is at least 98.5 wt.% Al.sub.2 O.sub.3, and

(b) the chromic oxide which is at least 95 wt.% Cr.sub.2 O.sub.3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Two different fusion-cast AZS refractories were employed in the crushed and screened form of grain in manufacturing fired refractory articles according to this invention. The chemistry and structure of those two fusion-cast AZS refractories were as follows:

______________________________________ AZS-1 AZS-2 ______________________________________ Al.sub.2 O.sub.3 wt. % 49.6 45.4 ZrO.sub.2 wt. % 33.5 40.4 SiO.sub.2 wt. % 15.2 12.9 Na.sub.2 O wt. % 1.5 1.1 Fe.sub.2 O.sub.3 wt. % 0.1 0.1 TiO.sub.2 wt. % 0.1 0.1 Glassy Phase wt. % 15-20 13-18 Glassy Phase vol. % 20-30 20-30 Crystal Phases Corundum Corundum Baddeleyite Baddeleyite ______________________________________

Each of the two fusion-cast AZS refractories were crushed and screened such that:

(1) the coarse grain had a cumulative particle size distribution as follows:

______________________________________ Tyler Particle Cumulative percent by weight Mesh Size left on screen No. (microns) Maximum Minimum ______________________________________ 6 3327 0 0 8 2362 32 12 10 1651 89 69 12 1387 99 84 20 833 99 89 ______________________________________

(2) the medium grain had a cumulative particle size distribution as follows:

______________________________________ Tyler Particle Cumulative percent by weight Mesh Size left on screen No. (microns) Maximum Minimum ______________________________________ 10 1651 0 0 14 1168 30 10 20 833 56 36 28 590 75 55 35 417 93 73 ______________________________________

and

(3) the fine grain has a cumulative particle size distribution as follows:

______________________________________ Tyler Particle Cumulative percent by weight Mesh Size left on screen No. (microns) Maximum Minimum ______________________________________ 35 417 0 0 65 208 43 23 100 147 54 34 150 105 63 43 200 74 71 51 250 62 73 53 325 44 80 60 ______________________________________

The alumina employed was ground to 95 wt.% -325 Tyler mesh and had the following typical chemistry (in wt.%): 99.2% Al.sub.2 O.sub.3, 0.45% Na.sub.2 O, 0.04% Fe.sub.2 O.sub.3, 0.02% SiO.sub.2 and 0.3% loss on ignition. However, lesser purity, low Na.sub.2 O aluminas may also be used.

The chromic oxide employed was all -325 Tyler mesh of about 98 wt.% Cr.sub.2 O.sub.3 pigment grade. However, lesser purity chromic oxide (e.g. metallurgical grade) may also be used.

EXAMPLE 1

A series of pressed and fired shapes having refractory compositions as set forth in Table 1 were prepared by mixing those compositions with suitable organic lubricant-binder (such as 0-0.3 wt.% water soluble polyethylene glycol wax and 1.75-3 wt.% lignin sulfite binder), forming the mixtures by hand ramming or mechanical pressing into shapes ranging from 5 lbs. brick to 1000 lbs. complicated shapes and thereafter firing the green shapes at 1500.degree.-1700.degree. C. for at least about six hours to develop ceramic bonding.

Similar fired properties are attainable by substitution of AZS-2 grain for the AZS-1 grain in the samples as shown in Table 1.

TABLER 1 __________________________________________________________________________ Sample Composition - Wt. % A B C D E F G __________________________________________________________________________ Refractory Composition Component Coarse AZS-1 grain 35 35 35 35 35 35 35 Medium AZS-1 grain 25 25 25 20 20 20 25 Fine AZS-1 grain 15 20 25 35 40 45 10 Alumina 25 20 15 10 5 -- 15 Chromic Oxide -- -- -- -- -- -- 15 1600.degree. C. Fired Properties Apparent Porosity - vol. % 16.1 16.7 14.5 15.5 16.3 17.5 17.0 Bulk Density - gms/cc. 3.16 3.16 3.17 3.17 3.14 3.11 3.16 Bulk Density - lbs./ft.sup.3 197 197 198 198 196 194 197 MOR at Room Temp. - psi 6100 5950 5900 6500 6750 5200 5600 MOR at 1340.degree. C. - psi 1300 1200 1500 1500 1550 1100 1425 Thermal Shock Cycles - room temp. 20+ 20+ 20+ 20+ 20+ 20+ 20+ to 1400.degree. C. and return to room temp. MOR at Room Temp. after thermal 3400 2650 1050 1400 1150 1600 900 Shock Cycling - psi. Apparent Porosity - vol. % 13 12 12.5 12 13 15 13 Bulk Density - gms/cc. 3.14 3.16 3.20 3.12 3.11 3.11 3.17 Bulk Density - lbs/ft..sup.3 196 197 200 195 194 194 198 MOR at Room Temp. - psi 8000 8350 7800 9350 8500 6950 6200 MOR at 1340.degree. C. - psi 800 900 950 1160 1150 1075 1300 Thermal Shock Cycles - room temp. 20+ 20+ 20+ 20+ 20+ 20+ 20+ to 1400.degree. C. and return to room temp. MOR at Room Temp. after thermal 1450 1500 1300 650 1100 1200 1050 Shock Cycling - psi. __________________________________________________________________________

For comparison, the following properties were obtained from a commercially available, competitive bonded AZS refractory with substantially identical oxide analysis like and believed to be that described in Canadian Pat. No. 754,627 as example #2 in Table I on page 8 thereof:

______________________________________ Apparent Porosity-vol.% 17.1 Bulk Density-gms./cc. 3.16 Bulk Density-lbs./ft..sup.3 197 MOR at Room Temp.-psi 1500 MOR at 1340.degree. C.-psi 750 Thermal Shock Cycles-Room Temp. to 1400.degree. C. to Room Temp. 20+ MOR at Room Temp. after Thermal Shock Cycling-psi 1100 ______________________________________

The notation of 20+ for thermal shock cycles means that no failure had yet occurred after 20 cycles.

Performance of pressed and fired refractory bodies of this invention in contact with common soda-lime and borosilicate glasses is illustrated by the comparative standard test results shown in Table 2 for Sample C of this invention and for the previously noted competitive pressed and bonded AZS refractory (designated Sample X). Typical analyses of those glasses are (in wt.%):

______________________________________ Soda-Lime Borosilicate ______________________________________ 72% SiO.sub.2 81% SiO.sub.2 14% Na.sub.2 O+K.sub.2 O 13% B.sub.2 O.sub.3 13% CaO+MgO 4% Na.sub.2 O 1% Al.sub.2 O.sub.3 2% Al.sub.2 O.sub.3 ______________________________________

Sample C is a preferred composition for contact with these types of glasses because the glassy phase in the original fusion-cast AZS grain used therein appears converted to mullite in the fired body to a greater degree than in the other samples. The tests and determination of data values for corrosion cut and stoning potential are described in U.S. Pat. Nos. 3,519,447 and 3,632,359. The corrosion ratings are derived from the corrosion cut data by arbitrarily assigning a rating of 100 for Sample C as a control standard and then calculating the rating for Sample X as a test sample as follows: ##EQU1## The test and determination of data values for blistering rating are described in U.S. Pat. No. 3,519,448. The data shows that the fired refractory body according to this invention has a much greater resistance to molten glass corrosion and to releasing stones and blisters into the molten glass.

Table 2 ______________________________________ Soda-Lime Glass Borosilicate Glass Test Conditions: 1450.degree. C.-3 days 1550.degree. C.-6 days Sample C X C X ______________________________________ Corrosion Cut at Melt Line-mm. 1.36 2.26 0.73 1.32 Corrosion Rating 100 60 100 55 Stoning Potential 1.20 2.48 0.6 0.9 Blister Rating -- -- 16 35 ______________________________________

Comparative data for corrosion test performance in molten glass of the type used to make wool-type glass fibers (designated Wool Glass) is given in Table 3 for two samples of this invention, a sample of solid fusion-cast AZS-1 refractory and a commercial pressed and bonded chromealumina refractory (designated Sample Y) presently used in contact with such molten glass. A typical analysis of Wool Glass is (in wt.%): 59% SiO.sub.2, 16% CaO, 11% Na.sub.2 O, 5.5% MgO, 4.5% Al.sub.2 O.sub.3, 3.5% B.sub.2 O.sub.3 and 0.5% K.sub.2 O. A typical analysis of the bonded chrome-alumina refractory is (in wt.%): 81.7% Al.sub.2 O.sub.3, 16.0% Cr.sub.2 O.sub.3, 0.8% P.sub.2 O.sub.3, 0.5% SiO.sub.2, 0.5% Fe.sub.2 O.sub.3 and 0.5% Na.sub.2 O. Based on AZS-1 as an arbitrary standard, Sample G containing chromic oxide shows superior performance to the commercial bonded refractory also containing chromic oxide. Since it is known that similar refractories containing chromic oxide commonly perform better with molten wool glass than those without chromic oxide, it is not surprising that Sample C exhibits poor corrosion resistance to molten wool glass.

Table 3 ______________________________________ Test Conditions; Wool Glass-1450.degree. C.-3 days Corrosion Rating Sample (at Melt Line) ______________________________________ AZS-1 100 G 129 C 0 (cut off) Y 64 ______________________________________

A fired article according to this invention can also be provided with good resistance to molten wool glass corrosion by employing grain of fusion-cast AZS refractory containing Cr.sub.2 O.sub.3. For example, a fusion-cast refractory of the following oxide analysis may be so employed to modify samples of this invention not otherwise containing chromic oxide: 28.3 wt.% Al.sub.2 O.sub.3, 28.0% Cr.sub.2 O.sub.3, 28.0 wt.% ZrO.sub.2, 14.6 wt.% SiO.sub.2 and 1.1 wt.% Na.sub.2 O (not including minor impurities present up to 0.3 wt.%).

By means of a static alkali resistance test, samples of this invention have been found to exhibit superior resistance ratings such as to indicate their good capability of longer service life as superstructure refractories in glass melting furnances and other similar applications. Samples were prepared by core drilling a one inch diameter hole to a depth of two inches in fired cube samples with faces 3 inches wide to form a crucible. Thirty grams of Na.sub.2 CO.sub.3 were placed within those crucible samples, each of which are then covered with a piece of the same fired refractory. Each test assembly is heat to 1500.degree. C. and held there for 7 days, after which it is cooled and cut vertically in half for examination and rating on an arbitrary performance scale ranging from 1 (no visible attack) to 10 (extreme exfoliation, cracking and dissolution of sample surface contacted by melted sodium carbonate to a depth of at least 3/16 - 1/4 inch). Table 4 shows comparative ratings illustrating the superior performance of pressed and fired refractories according to this invention.

Table 4 ______________________________________ Sample Alkali Resistance Rating ______________________________________ F 1 C 7 X 10 ______________________________________

EXAMPLE 2

A series of cast and fired refractory samples were prepared by compositions as described in Table 5. Each refractory composition was mixed with an ethyl silicate binder (7 wt.% in Samples H, I, K, L, M and 0 and 8 wt.% in Sample N) and 0.2 wt.% of triethanolamine as a reaction or gelling catalyst for the ethyl silicate binder. The ethyl silicate binder was reported by the manufacturer to contain 40.5-42.5 wt.% SiO.sub.2 in the clear water-white liquid having a specific gravity at 20.degree. C. of 1.050-1.080, maximum free ethanol of 1.5 wt.%, acidity as HCl of .ltoreq. 0.01 wt.%, density of 7.9 lbs./gal., freezing point of below -57.degree. C. and a flash point of 12.8.degree. C. Each mixture was then vibratory cast by known conventional techniques into a mold to form the desired shape. After gelling of the binder and removal from the mold, the cast shape was dried at about 93.degree. C. or somewhat higher for approximately eight hours or so. Thereafter the green dried shape was fired to 1550.degree.-1660.degree. C. for at least four hours.

It is to be understood that colloidal silica binder can be provided by sources other than as the residue of ethyl silicate binder. Any suitable alkyl silicate, silica sol or colloidal silica solution (or suspension) may be utilized. Desirably these collodial silica binders will be in amounts to provide 2-7 wt.% SiO.sub.2 residue in the refractory composition of this invention. Additionally, known alternative reaction or gelling catalysts may be employed with suitable gellable alkyl silicates.

The compositions in Table 5 may also be pressed into refractory articles if desired.

TABLE 5 __________________________________________________________________________ Sample Composition - Wt. % Refractory Composition Component H I K L M N O __________________________________________________________________________ Coarse AZS-1 grain 33 -- 33 37 33 33 33 Medium AZS-1 grain 37 -- 32 33 37 37 37 Fine AZS-1 grain 15 -- 25 -- 15 15 15 Alumina 15 15 10 30 10 5 15* Chromic Oxide -- -- -- -- 5 10 -- Coarse AZS-2 grain -- 33 -- -- -- -- -- Medium AZS-2 grain -- 37 -- -- -- -- -- Fine AZS-2 grain -- 15 -- -- -- -- -- (*A-2 alumina instead A-10 alumina as in other samples) 1600.degree. C. Fired Properties Apparent Porosity - vol. % 21.3 21 19.6 23.5 22 24 23 Bulk Density - lbs/ft..sup.3 185 188.5 183 182 186 182 183 MOR at Room Temp. - psi. 4450 3700 4100 3550 3400 3000 4000 MOR at 1340.degree. C. - psi. 1000 1000 1500 1350 200 500 1100 Thermal Shock Cycles - Room Temp. 20+ 20+ 20+ 20+ 20+ 20+ 20+ to 1400.degree. C. to Room Temp. MOR at Room Temp. after thermal 1950 850 1025 2400 900 1450 1600 Shock cycles - psi. __________________________________________________________________________

By way of comparison, the following properties were determined for a commercial competitive cast and fired refractory (designated Sample Z hereafter) made with Carbomul.sup..RTM. fused AZS grain (produced and sold by the Carborundum Company) believed to be in accordance with U.K. Pat. 1,429,723:

______________________________________ Apparent Porosity-vol.% 21 Density-lbs./ft..sup.3 180 MOR at Room Temp.-psi 2050 MOR at 1340.degree. C.-psi 1000 Thermal Shock Cycles-Room Temp. to 1400.degree. C. to Room Temp. 20+ MOR at Room Temp. after Thermal Shock Cycling-psi 1050 ______________________________________

Carbomul.sup..RTM. grain is reported by the manufacturer to have the following typical chemistry and structure:

______________________________________ Al.sub.2 O.sub.3 -47.00 wt. % Na.sub.2 O - 0.30 wt. % maximum ZrO.sub.2 -36.00 wt. % Fe.sub.2 O.sub.3 -0.20 wt. % maximum SiO.sub.2 -16.50 wt. % TiO.sub.2 -0.20 wt. % maximum Glassy phase - about 5 wt. % Crystal phases - Mullite Monoclinic zirconia ______________________________________

Comparative molten glass corrosion test data is shown in Table 6 for Samples H and Z. The data illustrates the superior corrosion resistance of this invention over prior art rebonded fused AZS grain products.

Table 6 ______________________________________ Soda-Lime Glass Test Conditions: 1350.degree. C. 2 days Sample: H Z ______________________________________ Corrosion Cut at Melt Line mm. 0.24 0.48 Corrosion Rating 100 50 ______________________________________

Samples H and Z were also subjected to the previously described static alkali resistance test. Sample H remained essentially unchanged by the molten sodium carbonate whereas Sample Z exhibited cracking and exfoliation as a result of the alkali attack.

Claims

1. Refractory composition for making refractory articles consisting of:

(A) 25-60 wt.% fusion-cast alumina-zirconia-silica refractory coarse grain being at least 89 wt.% -6+20 Tyler mesh,

(B) 0-38 wt.% fusion-cast alumina-zirconia-silica refractory medium grain being at least 73 wt.% -10+35 Tyler mesh, and

(C) 30-50 wt.% at least one component selected from the group consisting of

(1) 0-50 wt.% fusion-cast alumina-zirconia silica refractory fine grain being at least 60 wt.% -35+325 Tyler mesh, and

(2) 0-30 wt.% at least one constituent selected from the group consisting of

(a) alumina being at least 90 wt.% -325 Tyler mesh, at least 98.5 wt.% Al.sub.2 O.sub.3 and not more than 0.5 wt.% Na.sub.2 O, and

(b) -325 Tyler mesh chromic oxide being at least 95 wt. % Cr.sub.2 O.sub.3. the fusion-cast alumina-zirconia-silica refractory having:

(i) a three-phase microstructure of interlocking crystals of corundum phase and baddeleyite phase with intercrystalline glassy phase therebetween, the glassy phase being about 15-30 vol.% of the alumina-zirconia-silica refractory, and

(ii) an oxide analysis consisting of 35-60 wt.% Al.sub.2 O.sub.3 plus Cr.sub.2 O.sub.3 with Cr.sub.2 O.sub.3.ltoreq.60 wt.% of Al.sub.2 O.sub.3 plus Cr.sub.2 O.sub.3, 25-50 wt.% ZrO.sub.2, 10-18 wt.% SiO.sub.2, 0.8-1.8 wt.% Na.sub.2 O plus K.sub.2 O, and up to 0.7 wt.% other ingredients.

2. Refractory composition of claim 1 wherein the fusion-cast AZS refractory has an oxide analysis consisting of 40-55 wt.% Al.sub.2 O.sub.3 plus Cr.sub.2 O.sub.3 with Cr.sub.2 O.sub.3.ltoreq.50 wt.% of Al.sub.2 O.sub.3 plus Cr.sub.2 O.sub.3, 30-45 wt.% ZrO.sub.2, 10-16 wt.% SiO.sub.2 1.0-1.6 wt.% Na.sub.2 O + K.sub.2 O, and up to 0.5 wt.% other ingredients.

3. Refractory composition of claim 1 wherein the fusion-cast AZS refractory has an oxide analysis consisting of 40-55 wt.% Al.sub.2 O.sub.3, 30-45 wt.% ZrO.sub.2, 10-16 wt.% SiO.sub.2, 1.0-1.6 wt.% Na.sub.2 O, and up to 0.5 wt.% other ingredients.

4. Refractory composition of claim 1 wherein the fusion-cast AZS refractory has:

(A) about 20-30 vol.% glassy phase, and

(B) an oxide analysis consisting of 45-50 wt.% Al.sub.2 O.sub.3, 33-41 wt.% ZrO.sub.2, 12-16 wt.% SiO.sub.2, 1.1-1.5 wt.% Na.sub.2 O and up to 0.3 wt.% other ingredients.

5. Refractory composition of claim 1 wherein:

(A) the coarse grain is 33-37 wt.%,

(B) the medium grain is 20-25 wt.%, and

(C) the at least one component is 40-45 wt.% selected from the group consisting of

(1) 15-45 wt.% the fine grain and

(2) 0-30 wt.% the at least one constituent selected from the group consisting of

(a) the alumina which is at least 98.5 wt.% Al.sub.2 O.sub.3 and

(b) the chromic oxide which is at least 95 wt.% Cr.sub.2 O.sub.3.

6. Refractory composition of claim 1 wherein:

(A) the coarse grain is 33-37 wt.%,

(B) the medium grain is 32-37 wt.%, and

(C) the at least one component is 30-35 wt.% selected from the group consisting of

(1) 0-25 wt.% the fine grain and

(2) 10-30 wt.% the at least one constituent selected from the group consisting of

(a) the alumina which is at least 98.5 wt.% Al.sub.2 O.sub.3, and

(b) the chromic oxide which is at least 95 wt.% Cr.sub.2 O.sub.3.

7. Fired refractory article having a fourphase micro-structure of corundum, badeleyite mullite and glassy phase with the mullite being about 5-25 wt.% thereof and the glassy phase being about 5-20 vol.% thereof, the article being a sintered refractory composition consisting of:

(A) 25-60 wt.% fusion-cast alumina-zirconia-silica refractory coarse grain being at least 89 wt.% -6+20 Tyler mesh,

(B) 0-38 wt.% fusion-cast alumina-zirconia-silica refractory medium grain being at least 73 wt.% -10+35 Tyler mesh,

(C) 30-50 wt.% at least one component selected from the group consisting of

(1) 0-50 wt.% fusion-cast alumina-zirconia-silica refractory fine grain being at least 60 wt.% -35+325 Tyler mesh, and

(2) 0-30 wt.% at least one constituent selected from the group consisting of

(a) alumina being at least 90 wt.% -325 Tyler mesh, at least 98.5 wt.% Al.sub.2 O.sub.3 and not more than 0.5 wt.% Na.sub.2 O, and

(b) -325 Tyler mesh chromic oxide being at least 95 wt.% Cr.sub.2 O.sub.3, and

(D) 0-7 wt.% colloidal silica, the fusion-cast alumina-zirconia-silica refractory having:

(i) a three-phase microstructure of interlocking crystals or corundum phase and baddeleyite phase with intercrystalline glassy phase therebetween, the glassy phase being about 15-30 vol.% of the alumina-zirconia-silica refractory, and

(ii) an oxide analysis consiting of 35-60 wt.% Al.sub.2 O.sub.3 plus Cr.sub.2 O.sub.3 with Cr.sub.2 O.sub.3.ltoreq. 60 wt.% of Al.sub.2 O.sub.3 plus Cr.sub.2 O.sub.3, 25-50 wt.% ZrO.sub.2, 10-18 wt.% SiO.sub.2, 0.8-1.8 wt.% Na.sub.2 O plus K.sub.2 O, and up to 0.7 wt.% other ingredients.

8. Refractory composition of claim 3 wherein selected constituent alumina is at least 5 wt.% and selected constituent chromic oxide is at least 5 wt.%.

9. Fired refractory article of claim 7 wherein the fusion-cast AZS refractory has an oxide analysis consisting of 40-55 wt.% Al.sub.2 O.sub.3, 30-45 wt.% ZrO.sub.2, 10-16 wt.% SiO.sub.2, 1.0-1.6 wt.% Na.sub.2 O, and up to 0.5 wt.% other ingredients.

10. Fired refractory article of claim 9 wherein selected constituent alumina is at least 5 wt.% and selected constituent chromic oxide is at least 5 wt.%.